1. Field of the Invention
The present invention relates to a conductive composition and production method thereof. The present invention further relates to an antistatic coating material for imparting antistatic properties to a film, an antistatic coating material having antistatic properties, an antistatic film used in wrapping materials of food and electronic parts, an optical filter used for the front surface of a liquid crystal display and a plasma display, and an optical information recording medium, such as CDs and DVDs. The present invention relates to capacitors such as an aluminum electrolytic capacitor, tantalum electrolytic capacitor, and niobium electrolytic capacitor and a production method thereof.
The present invention claims priority on Japanese Patent Application No. 2004-274992, filed on Sep. 22, 2004, Japanese Patent Application No. 2004-337468, filed on Nov. 22, 2004, and Japanese Patent Application No. 2004-348684, filed on Dec. 1, 2004, the contents of which is incorporated herein by reference.
2. Related Art
In recent years, conductive polymers in which electron-donating compounds or electron-accepting compounds (dopants) are added (doped) to conductive polymers such as polypyrrole, polythiophene, polyacetylene, poly-p-phenylene, and polyaniline have been developed.
Two types of doping, i.e., p-type doping wherein an electron-donating compound (oxidant) is doped to generate numerous holes in a conductive polymer and the holes are made conductive as carriers and an n-type doping wherein an electron-donating compound (reductant) is doped to generate numerous electrons in a conductive polymer and the electrons are made conductive as carriers.
The above conductive polymers are usually prepared by an electrolytic polymerization method or a chemical oxidative polymerization method.
The electrolytic polymerization method is a process wherein a mixed solution of an electrolyte as dopant and a monomer which can form a conductive polymer is electrolytically polymerized on an electrode to form a conductive polymer into a film on the electrode. This electrolytic polymerization method is difficult to prepare the conductive polymer in large quantities because the monomer is polymerized on the electrode, in addition, the obtained film has low solvent solubility making it difficult to use in the industry.
In contrast, the chemical oxidative polymerization method is not restricted as is the electrolytic polymerization method. Namely, a large quantity of conductive polymer can be obtained in a solution by adding an appropriate oxidant and an appropriate oxidative polymerization catalyst to a monomer which can form a conductive polymer. However, in the chemical oxidative polymerization method, the solubility for solvents decreases with the growth of main chain of conductive polymer; therefore, the polymer is obtained in an insoluble solid powder in many cases. It is difficult to form a uniform conductive film on a base with the insolubility in solvents.
A solubilization made by introducing a functional group into a conductive polymer and a solubilization made by dispersion in a binder resin, and solubilization using an anion-containing polymeric acid, and the like have been attempted. However, it was difficult to ensure high electric conductivity, compatibility with a binder resin, and heat stability in these methods.
A method wherein a conducting layer is provided on a base surface by dissolving an oxidant and a monomer forming a conductive polymer with a vinyl chloride copolymer in a solvent and applying it to the base surface, and polymerizing the monomer to form a complex of a vinyl chloride copolymer and a conductive polymer while controlling the oxidation potential with a solvent has been proposed as a method for forming a conducting layer on a base provided on a solid surface of polymer molding (see Japanese Unexamined Patent Application, First Publication No. 5-186619).
However, in the method described in Japanese Unexamined Patent Application, First Publication No. 5-186619, the polymerization of monomer by oxidation potential control is restricted due to the fact that a solvent is limited according to the kind of base; therefore, high electric conductivity cannot be ensured. Containing a vinyl chloride copolymer as an insulative resin also becomes a reason why high electric conductivity cannot be ensured.
Moreover, a method wherein 3,4-dialkoxythiophene is polymerized by chemical oxidation to produce a poly(3,4-dialkoxythiophene) solution with an oxidant in the presence of polystyrene sulfonic acid having a molecular weight of 2000 to 500000 has been proposed for the purpose of improving the dispersibility of an conductive polymer in water (see Japanese Patent Publication No. 2636968).
However, in the method described in Japanese Patent Publication No. 2636968, a conductive polymer can be easily dispersed in water, but it contains more polymeric acid having an anion group to improve the water dispersibility of the conductive polymer in this method. Therefore, there is the problem that high electric conductivity is hard to obtain.
Furthermore, a preparation method that a sulfonated substance usable as antioxidant and a compound having an analogous structure, which are as a dopant and a heat stabilizer, are mixed with a monomer, and then, electrolytically polymerized for the purpose of increasing the heat stability of a conductive polymer has been proposed (see Japanese Patent Publication No. 2546617).
However, the method described in Japanese Patent Publication No. 2546617 has the problem that heat stability is obtained but solvent solubility is hard to obtain.
In some cases, π conjugated conductive polymers are used as an organic material which has a conductive mechanism of electronic conduction.
Resin films themselves are insulators and easily electrically charged. Furthermore, resin films tend to charge static electricity by friction or the like. Moreover, static electricity is not easily removed, but rather accumulates causing various problems.
Particularly, when a resin film is used for food packaging material emphasizing sanitary properties, dust and dirt are absorbed in display, the appearance is significantly impaired and in some cases the commodity value is lowered. When resin film is used for packaging a powder, charged powder is absorbed or repulsed in its packaging or use, and therefore causes the inconvenience that handling of the powder becomes difficult. When a precision electronic part is packaged with a resin film, it is a feared that the precision electronic part is damaged by the static electricity; therefore, the occurrence of static electricity must always be prevented.
Moreover, it is desirable that the surface of an optical filter or an optical information recording medium has high hardness and high transparency as well as antistatic properties to prevent the adherence of dust and dirt due to the static electricity. Particularly, it is desired that the surface resistance of the antistatic property be in the region of about 106 to 1010Ω and that the resistance stabilizes (i.e., stabilized antistatic properties), from which antistatic coating having antistatic properties and high hardness is provided on the surface of optical filter or optical information recording medium.
In order to impart antistatic properties, for example, a method for coating a resin film or a surfactant on the surface and a method for kneading a surfactant into a resin forming a resin film or an antistatic coating have been adopted (for example, see “Fine Chemical Antistatic Agents Latest Market Trend (the first volume),” Vol. 16, No. 15, 1987, p. 24-36, published by CMC).
However, electrostatic prevention based on this surfactant has the drawback that its conduction mechanism is one of ion conduction, therefore, it is easily affected by humidity, conductivity increases by high humidity; however, conductivity decreases by low humidity. Therefore, the antistatic function deteriorates and antistatic performance is not displayed as necessary in an environment where the humidity is low, and especially static electricity easily occurs.
If a metal or carbon with electron conduction as conduction mechanism is used, such humidity dependence disappears, but these materials are totally opaque and not applicable for purposes requiring the transparency.
Moreover, a metal oxide such as ITO (Indium Tin Oxide) has transparency and adopts the electron conduction as a conduction mechanism; therefore, it is suited in this respect, but a process using a sputtering apparatus must used for its film-forming. Not only is the process complicated but also the manufacturing cost rises. A coating film of inorganic metal oxide has low flexibility. When a film is formed on a thin base film, the coating film may be broken and does not exhibit conductivity. In addition, it is feared that peeling occurs at the interface and the transparency reduces because the adhesion to the base being an organic substance is low.
Moreover, π conjugated conductive polymers are known as organic materials with electron conduction as the conduction mechanism, but the π conjugated conductive polymers generally have insoluble and infusible properties, and it is difficult to coat the polymers on a base film after polymerization. Accordingly, it has been attempted that aniline be polymerized in the presence of a polymeric acid with a sulfo group to form a water-soluble polyaniline, the obtained mixture is used, coated on a base film and then dried (e.g., see Japanese Unexamined Patent Application, First Publication No. 1-254764).
However, as with the method described in Japanese Unexamined Patent Application, First Publication No. 1-254764, if aniline is directly polymerized on a base, an antistatic coating can be formed. In this case, the antistatic coating has low conductivity because the coating is not obtained by a π conjugated conductive homopolymer, and the adhesion to a resin base is low and manufacturing processes are also complicated because the antistatic coating is water-soluble.
Capacitors are given as example of using π conjugated conductive polymers.
In recent years, it has been required to reduce the impedance of capacitors used for electronics in a high-frequency region with the digitalization of electronics. A so-called functional capacitor in which an oxide film of valve metals such as aluminum, tantalum, and niobium is adopted as a dielectric and a π conjugated conductive polymer is formed on this surface and used as a cathode and thus far has been used in response to this requirement.
As shown in Japanese Unexamined Patent Application, First Publication No. 2003-37024, it is general that the structure of this functional capacitor has an anode consisting of a valve metal porous body, a dielectric layer formed by oxidizing the surface of anode, and a cathode obtained by laminating a solid electrolyte layer, a carbon layer and a silver layer on the dielectric layer. The solid electrolyte layer of the capacitor is a layer constructed from a π conjugated conductive polymer of pyrrole, thiophene, and the like, and the layer performs to penetrate into the inside of porous body, come into contact with a larger area of electrolyte layer to derive a high capacity, restore defects of the dielectric layer, and prevent leakage of a current.
An electrolytic polymerization method (see Japanese Unexamined Patent Application, First Publication No. 63-158829) and a chemical oxidative polymerization method (see Japanese Unexamined Patent Application, First Publication No. 63-173313) have been widely known as methods for forming the π conjugated conductive polymers.
However, the electrolytic polymerization method has the problem that a conductive layer made of manganese oxide must be formed on the surface of the valve metal porous body beforehand, the process is complicated, and further the manganese oxide has low conductivity and weakens the effect of using the π conjugated conductive polymers having high conductivity.
The chemical oxidative polymerization method has the problem that the polymerization time is long, the polymerization must be repeated to ensure the thickness, the production efficiency of capacitors is low and the conductivity is also low.
Accordingly, a method wherein conductive polymers are not formed by the electrolytic polymerization method and the chemical oxidative polymerization method (see Japanese Unexamined Patent Application, First Publication No. 7-105718) has been proposed. A method wherein aniline is polymerized while allowing a polymeric acid with a sulfo group or carboxyl group to coexist to form a water-soluble polyaniline, the aqueous solution of polyaniline is coated on a base film and then dried has been described in Japanese Unexamined Patent Application, First Publication No. 7-105718. This preparation method is simple, but the permeability for the inside of porous body of the polyaniline solution deteriorates, the conductivity is low because the polymeric acid is contained except for the π conjugated conductive polymer and the humidity dependence on conductivity is also found by the effect of polymeric acid.
A capacitor having a low equivalent series resistance (ESR) as index of impedance has been desired, and the conductivity of the solid electrolyte layer must be increased to decrease ESR. As a method for increasing the conductivity of the solid electrolyte layer, for example, it has been proposed to highly control conditions for the chemical oxidative polymerization method (see Japanese Unexamined Patent Application, First Publication No. 11-74157). However, in the production method, the complex chemical oxidative polymerization method is more complicated in many cases, thus the simplification and low costing of processes cannot be realized.